1. Field of the Invention
The present invention relates to a liquid-sealing type vibration isolating apparatus which gives a vibration isolating effect on the basis of the flowing action of a fluid (liquid) sealed therein. More particularly, the present invention relates to a liquid-sealing type vibration isolating apparatus in which the liquid in a liquid chamber is vibrated at a certain frequency, the vibrating apparatus thereof having a simple structure, and isolation of vibration of a plurality of kinds is effectively accomplished over a wide scope ranging from low to high frequency regions.
2. Description of the Related Art
A vibration isolating apparatus, particularly an automotive engine mount must be capable of coping with a wide range of frequencies because the engine serving as a power source is used under various conditions ranging from idling operation to the maximum velocity of revolutions. For this purpose, there has already been invented an apparatus known as a liquid-sealing type engine mount (vibration isolating apparatus) in which two liquid chamber are provided and are connected with an orifice, such as the one disclosed in Japanese Unexamined Patent Publication No. 4-60231.
The aforesaid known apparatus is designed to have two orifices to cope with two kinds of input frequency within the low-frequency region. The apparatus can cope (vibration isolation) with two kinds of vibration such as engine idling vibration and engine shaking by operating these two orifices. These kinds of vibration have however a frequency with a range of from 10 to 30 Hz. An automobile engine is used under diverse and various circumstances, and the range of frequencies of vibration and noise propagating through the engine and the engine mount supporting the engine covers a wide region. Recently, in particular, vibration and noise associated with engine noise including a dull sound which is a vibration within the higher frequency region, in addition to the foregoing idling vibration and engine shake are forming an issue.
More recently, tuning of an engine mount is becoming more common with a view to isolating a dull sound associated with vibration of a relatively high frequency within a range of from 100 to 600 Hz. For the purpose of coping with a plurality of conditions as described above, there has already been known a liquid-sealing type vibration isolating apparatus having a liquid chamber and a fluid bag to change the volume at a specific frequency within the fluid bag, as disclosed, for example, in Japanese Patent Publication No. 6-29634.
In this known apparatus, the fluid bag is provided in the liquid chamber to change the volume thereof at a prescribed frequency, thereby causing a liquid in the liquid chamber on the vibration input side to flow via an orifice toward another side liquid chamber. More specifically, in the low-frequency region mainly comprising idling vibration, the liquid pressure in the liquid chamber on the vibration input side is increased so as to obtain a high damping property. In the high-frequency region, on the other hand, increase in the liquid pressure in the liquid chamber on the vibration input side is avoided to obtain a low dynamic spring constant. For recent automotive engine mounts, however, a vibration isolating apparatus should cover idling vibration against which resonance phenomenon should be avoided by reducing the dynamic constant as vibration within the low-frequency region, and vibration associated with engine shaking against which vibration should be inhibited by increasing the damping property.
Further, in this known apparatus, a fluid pressure generating device is need for causing the volume thereof to be changed, so that there are raised the following problems.
(1) An additional space has to be secured in an engine room.
(2) The apparatus itself increases a production cost.
In order to achieve a vibration isolating apparatus capable of coping with these contradictory conditions, simple vibrating of the liquid in the liquid chamber on the vibration input side in the same or reversed phase is insufficient.
To cope with these multiple conditions, furthermore, there is already known an apparatus called a voice-coil type liquid-sealing type vibration isolating apparatus in which a liquid chamber is provided and which has a vibrator comprising a voice coil or the like vibrating at a certain frequency in the liquid chamber, as disclosed, for example, in Japanese Unexamined Patent Publication No. 5-149369. An apparatus of this type has however inevitably a complicated structure because of the necessity of a plurality of liquid chambers, a movable piece comprising a piston or the like in the liquid chamber and a voice coil for driving such a movable piece. The vibration isolating apparatus as a whole becomes unavoidably heavier because of shaking coils, permanent magnets and many other parts.
The present invention was developed to solve the problems as described above, and has an object to provide a vibration isolating apparatus capable of certainly inhibiting vibration occurring from a vibrating body from propagating in the vehicle room.
Another object of the present invention is to provide a liquid-sealing type vibration isolating apparatus permitting giving a low dynamic spring constant even in the high frequency region for the purpose of isolating vibration in a relatively high frequency region.
Further another object of the present invention is to provide a liquid-sealing type vibration isolating apparatus which can give a low dynamic spring constant (low dynamic spring property) for both vibration in a low-frequency region mainly comprising idling vibration and vibration in a high-frequency region causing a dull sound, and give a high damping property against vibration in a low-frequency region coming from engine shake.
To achieve these objects, according to the present invention, a liquid-sealing type vibration isolating apparatus is provided which comprises a coupler attached to a vibrating body, a holder attached to the vehicle body side, an insulator which is provided between the coupler and the holder and absorbs and isolates vibration from the vibrating body, and a vibration isolating mechanism which directly follows the insulator and is formed with a liquid chamber sealing a liquid which is an incompressible fluid; the vibration isolating mechanism comprising a main chamber having a wall thereof formed by a part of the insulator and sealing the liquid, an auxiliary chamber connected to the main chamber so that the liquid flows through an orifice, an equilibrium chamber which is provided at a part of the main chamber via a diaphragm and is formed so that the volume thereof in the chamber changes, and an air chamber which surrounds the auxiliary chamber via another diaphragm and constantly receives air; wherein there are further provided switching means which conducts a switching operation so as to alternately introduce any one of a negative pressure and the atmospheric pressure into the equilibrium chamber having the aforesaid construction constantly or in synchronization with engine vibration, and in addition, control means which controls the switching operation of the switching means.
By adopting the constitution as described above, the following effects are available in the present invention. In the present invention, more specifically, an equilibrium chamber is provided via a diaphragm in the main chamber, and a negative pressure or the atmospheric pressure is appropriately introduced into the equilibrium chamber. Introduction of the negative pressure or the atmospheric pressure is accomplished through switching means under control by the control means. That is, operation of this switching means causes the negative pressure to be periodically introduced at a certain frequency or causes a certain negative pressure to be continuously introduced. As required, the equilibrium chamber is kept in a state open to the open air. Therefore, in response to idling vibration of the engine forming a vibrating body, the pressure (volume) of the equilibrium chamber is altered through an ON/OFF operation of the switching means, thereby absorbing fluctuations of the liquid pressure in the main chamber caused by idling vibration entered via the insulator. This results in a reduced dynamic spring constant of the spring system formed by the insulator and the vibration isolating mechanism. Idling vibration is thus absorbed and isolated.
To cope with high-frequency vibration within a range of from 100 to 600 Hz causing a dull sound, which is a problem during travel of a vehicle, the switching means is operated to bring the equilibrium chamber into a state open to the open air. As a result, the volume in the equilibrium chamber freely changes relative to high-frequency vibration entered via the insulator and the liquid in the liquid chamber. This permits free vibration of the insulator and the liquid in the liquid chamber, whereby the dynamic spring constant of the spring system formed by the vibration isolating mechanism is inhibited to a low level. An improved isolating effect is thus available against high-frequency vibration. In the present invention, as described above, the switching means comprising a switching valve or the like, the orifice and the equilibrium chamber permit absorption and isolation of multiple kinds of vibration.
The liquid is allowed to flow through an orifice connecting the main chamber and the auxiliary chamber to isolate engine shake which is vibration of a frequency further lower than idling vibration, thereby absorbing and isolating the engine shake. More specifically, since vibration associated with engine shake has a frequency of about 10 Hz, it is difficult to isolate vibration by reducing the dynamic spring constant. In the present invention, therefore, a certain negative pressure is introduced into the equilibrium chamber forming the vibration isolating mechanism so as to bring the volume of the equilibrium chamber to null. This allows the liquid to flow through an orifice formed between the main chamber and the auxiliary chamber, and viscous drag resulting from the liquid causes production of a prescribed damping force. This damping force leads to damping of engine shake.
In another means for achieving the foregoing objects, a vibration isolating mechanism comprising a liquid chamber and the like is provided in series with the insulator. More particularly, there is provided a liquid-sealing type vibration isolating apparatus, wherein the vibration isolating mechanism comprises a main chamber which comprises a liquid chamber arranged in series with the insulator and having a wall thereof formed by a part of the insulator, an auxiliary chamber connected to the main chamber so as to allow the liquid to flow via an orifice to the main chamber and separated by a partition plate comprising a rigid body from the main chamber, an equilibrium chamber formed via a diaphragm between the main chamber and the partition plate and arranged so as to introduce any one of the atmospheric pressure and a negative pressure, and an air chamber provided under the auxiliary chamber via another diaphragm and constantly fed with air. By adopting this configuration, in the present invention, vibration from the vibrating body is transmitted directly to the insulator and the liquid in the main chamber, thus further improving the vibration isolating effect, in addition to the foregoing means. A vibration isolating apparatus having an equilibrium chamber in the main chamber is formed on the basis of the conventional upright-type liquid-sealing type vibration isolating apparatus, thus permitting improvement of assembly merit of the vibration isolating apparatus as a whole.
The aforesaid objects are achieved according to the present invention also by the vibration isolating apparatus, wherein the length L1 of a duct line from the atmospheric pressure inlet to the equilibrium chamber is set at a value determined by the following formula:
0.85 cT/4xe2x89xa6L1xe2x89xa61.15 cT/4 
where c is the sound velocity (340 m/sec) and T is a period of time (in seconds) during which the open air is introduced into the equilibrium chamber by the switching means.
The foregoing objects are achieved, according to the present invention, in the vibration isolating apparatus of the above-mentioned configuration, by providing an expansion chamber having a larger diameter than that of the duct line between the atmospheric pressure inlet and the switching means and setting the length L2 between the expansion chamber and the equilibrium chamber at a value determined by the following formula:
0.85 cT/4xe2x89xa6L2xe2x89xa61.15 cT/4 
where c is the sound velocity (340 m/sec) and T is a period of time (in seconds) during which the open air is introduced into the equilibrium chamber by the switching means.
According to the vibration isolating apparatus of the present invention, furthermore, the coupler attached to the vibrating body and the insulator provided between the coupler and the holder attached to the vehicle body side absorb most of vibration transmitted from the vibrating body. The vibration isolating mechanism following directly the insulator further controls and absorbs vibration. In other words, the liquid sealed in the main liquid chamber and the auxiliary liquid chamber flows through the orifice under the effect of vibration, and this flow controls and absorbs vibration. At the same time, a negative pressure introduced from the negative pressure source and the atmospheric pressure introduced from the atmospheric pressure inlet are alternately introduced into the equilibrium chamber provided in a portion of the main liquid chamber via a diaphragm. This introduction is accomplished by a switching operation of the switching means under control by the control means at a frequency f required for synchronizing with vibration of the aforesaid vibrating body. This alternate introduction permits alternate introduction of the negative pressure and the atmospheric pressure at a frequency corresponding to the required frequency, and in response to this, the pressure in the equilibrium chamber, and hence the volume thereof change. This change in volume positively controls and absorbs changes in the liquid pressure in the main liquid chamber produced by vibration of the vibrating body and entered via the insulator.
Because the switching means is switched over by switching, this switching may cause generation of a harmonic component. In the present invention, however, the length L1 of the duct line from the atmospheric pressure inlet to the equilibrium chamber is set at a value determined by the following formula:
0.85 cT/4xe2x89xa6L1xe2x89xa61.15 cT/4 
where c is the sound velocity (340 m/sec) and T is a period of time (in seconds) during which the open air is introduced into the equilibrium chamber by the switching means. A pulse may therefore be produced in the air introduced from the atmospheric pressure inlet, resulting in a temporary inertial supercharging. A pressure higher than the atmospheric pressure would thus be introduced into the equilibrium chamber. In parallel with this, the pressure waveform is corrected, thus resulting in elimination of the unnecessary harmonic component. Fluctuations of pressure in the equilibrium chamber therefore change into smooth behavior like a sine wave, hence permitting control of fluctuations of liquid pressure in the main liquid chamber in response to vibration of the vibrating body.
This is particularly effective when the length L1 of the duct line from the open air inlet to the equilibrium chamber cannot be set within the foregoing range. According to the present invention, an expansion chamber having a diameter larger than that of the duct line is provided between the open air inlet and the switching means and the length L2 of the duct line from the expansion chamber to the equilibrium chamber is set at a value determined by the following formula:
0.85 cT/4xe2x89xa6L2xe2x89xa61.15 cT/4 
where c is the sound velocity (340 m/sec) and T is a period of time (in seconds) during which the open air is introduced into the equilibrium chamber by the switching means. By only appropriately adjusting the length L2 of the duct line from the expansion chamber to the equilibrium chamber, therefore, the effect substantially the same as above is available. Therefore, when the length L1 of the duct line from the open air inlet to the equilibrium chamber cannot be set within the above range because of a particular necessity in piping, it suffices to provide an expansion chamber having a length L2 satisfying the above formula.
In addition, in the vibration isolating apparatus of the present invention, the required frequency is the one required for synchronizing with an idling vibration of the engine.
Further, the liquid-sealing type vibration isolating apparatus for achieving another object of the present invention comprises a main chamber having a wall thereof formed by a part of the insulator and receiving vibration directly propagating from the insulator, an auxiliary chamber connected to the main chamber via a small-diameter orifice so as to allow the liquid to flow and separated by a first partition plate comprising a rigid body from the main chamber, and an equilibrium chamber formed via a diaphragm between the main chamber and the first partition plate and receiving any one of a negative pressure and the atmospheric pressure; and the liquid-sealing type vibration isolating apparatus further comprising a second partition plate serving also as a stopper, provided in the main chamber above the diaphragm forming the equilibrium chamber, a second orifice comprising a large-diameter orifice in a portion of the second partition plate, switching means for performing a switching operation so as to alternately introduce any one of the negative pressure and the atmospheric pressure into the equilibrium chamber, in synchronization with engine vibration, and control means for controlling the switching operation of the switching means.
This constitution provides the following functions. First, as to idling vibration, the negative pressure and the atmospheric pressure are alternately introduced at a specific frequency into the equilibrium chamber provided under the main chamber by operating the switching means. That is, the pressure (volume) in the equilibrium chamber is altered by ON/OFF-operating the switching means, thereby absorbing fluctuations of liquid pressure in the main chamber caused by idling vibration entered via the insulator. This reduces the dynamic spring constant of the spring system formed by the insulator and the vibration isolating mechanism. This permits absorption and isolation of idling vibration.
As to engine shake which is vibration of a frequency further lower than that of idling vibration, the liquid is caused to flow through the small-diameter orifice connecting the main chamber and the auxiliary chamber, thereby absorbing and isolating engine shake. More specifically, because engine shake vibration has a frequency of about 10 Hz, it is difficult to isolate vibration by reducing the dynamic spring constant. In the present invention, therefore, the volume of the equilibrium chamber is kept null by continuously introducing a certain negative pressure into the equilibrium chamber forming the vibration isolating mechanism. This allows the liquid to flow through the small-diameter orifice formed between the main chamber and the auxiliary chamber, thereby causing generation of a prescribed damping force under the effect of viscous drag resulting from the flow of the liquid. Engine shake is thus damped by the action of this damping force.
On the other hand, with respect to the vibration of a high frequency of about 100 to 600 Hz which causes a dull sound during travel of a vehicle, the switching means is operated to bring the equilibrium chamber into the state open to the open air. The volume in the chamber can thus freely change in response to vibration of a frequency entered via the insulator and the liquid in the main chamber. The liquid in the main chamber is allowed to freely flow through the large-diameter orifice (second orifice) of the second partition plate provided in the main chamber, thus reducing the dynamic spring constant of the spring system formed by the vibration isolating mechanism to a low level. The isolating effect against vibration in the high-frequency region is thus improved. In the present invention, as described above, multiple kinds of vibration can be absorbed and isolated under the effect of the equilibrium chamber capable of changing the inner volume thereof by operating the switching means comprising a switching valve or the like.
In the present invention, the second partition plate comprising a rigid body is provided above the diaphragm forming the equilibrium chamber in the main chamber. When vibration entered from the vibrating body has a large amplitude, the downward stroke of the upper coupling member caused by this vibration from the vibrating body is arrested at this second partition plate. In other words, the second partition plate serves as an inner stopper of this vibration isolating apparatus. Under the effect of this stopper function, the diaphragm forming the equilibrium chamber is protected upon input of vibration. As a result, the change in volume of the equilibrium chamber is kept normal, thus permitting reduction of the dynamic spring constant.
In the liquid-sealing type vibration isolating apparatus for achieving further another object of the present invention, the vibration isolating mechanism comprises a liquid chamber sealing an incompressible fluid, an equilibrium chamber receiving a negative pressure or the atmospheric pressure, and an elastic diaphragm partitioning the liquid chamber and the equilibrium chamber; a plurality of said vibration isolating mechanisms are provided; a first liquid chamber provided in a first liquid chamber provided in a first vibration isolating mechanism from among these plurality of vibration isolating mechanisms and a second liquid chamber provided in a second vibration isolating mechanism are connected with a large-diameter orifice; the first liquid chamber provided in the first vibration isolating mechanism and a third liquid chamber provided in a third vibration isolating mechanism are connected with a small-diameter orifice; any one of a negative pressure and the atmospheric pressure is continuously introduced into a first equilibrium chamber provided in the first vibration isolating mechanism via switching means alternately in synchronization with engine vibration; and any one of a negative pressure and the atmospheric pressure is continuously introduced into a second equilibrium chamber provided in the second vibration isolating mechanism in compliance with a switching operation of the switching means in response to the traveling state of the vehicle.
By adopting the foregoing constitution, the following effects are available in the present invention. Vibration from the vibrating body is transmitted via the coupling member to the insulator made of a rubber material or the like. The insulator vibrates or deforms as a result and absorbs or isolates most of the entered vibration. While most of the vibration is thus isolated at the insulator, a part thereof is not isolated at the insulator, but is isolated at the vibration isolating mechanism following the insulator. Now, detailed operations of the individual vibration isolating mechanisms will be described below. First, the vibration isolating function against engine idling vibration will be described. In this case, the frequencies to be covered range from about 20 to 40 Hz. A negative pressure is therefore introduced through the switching means into the second equilibrium chamber in FIG. 1 to bring the volume of the second equilibrium chamber to null. That is, the diaphragm in the second vibration isolating mechanism is kept inoperable. In this state, a negative pressure and the atmospheric pressure are alternately introduced into the first equilibrium chamber of the first vibration isolating mechanism at a certain cycle (frequency). As a result, the liquid in the first liquid chamber provided under the insulator is about to flow through the small-diameter orifice to the third liquid chamber. However, because the negative pressure or the atmospheric pressure is introduced into the first equilibrium chamber so that the diaphragm is applied with vibration at a frequency higher than the liquid resonance frequency of the liquid present in the orifice, the liquid in the first liquid chamber does not flow toward the small-diameter orifice. The status of the liquid pressure in the first liquid chamber largely fluctuates, and the liquid in the first liquid chamber is vibrated in the same phase as the entered vibration. This inhibits increase in the dynamic spring constant in the present vibration isolating apparatus. That is, reduction of the dynamic spring constant is successfully achieved.
As to engine shake which is vibration caused during travel of a vehicle and has a frequency further lower than the idling vibration, a negative pressure is introduced into the first equilibrium chamber to bring the volume of the first equilibrium chamber to null. In other words, the diaphragm of the first vibration isolating mechanism is kept inoperable. In this state, when vibration is transmitted from a vibrating body such as an engine to the upper coupling member, the liquid pressure in the first liquid chamber increases, and the liquid in the first liquid chamber flows through the large-diameter orifice to the second liquid chamber of the second vibration isolating mechanism. The flow of the liquid in the first liquid chamber through the large-diameter orifice makes it available a high damping property. As a result, vibration of engine shake having a frequency of about 10 Hz is inhibited. Vibration caused upon engine cranking, or vibration of a large amplitude caused upon sudden start or sudden acceleration, which is vibration of a large amplitude at a further lower frequency is inhibited under the effect of the small-diameter orifice. The small-diameter orifice causes the liquid in the first liquid chamber to flow to the third liquid chamber against input of an initial load caused upon installation on the vibrating body, to keep balance of inner pressure in the individual liquid chambers.
As to vibration within a high frequency region of from 100 to 600 Hz, which poses the problem of a dull sound in the vehicle room, the atmospheric pressure is introduced into the first equilibrium chamber of the first vibration isolating mechanism to bring the first equilibrium chamber into the state open to the open air. At the same time, a negative pressure is continuously introduced into the second equilibrium chamber forming the second vibration isolating mechanism to bring the volume of the second equilibrium chamber to null. The vibration transmitted through the upper coupling member into the first liquid chamber consequently vibrates the liquid in the first liquid chamber. However, since the first equilibrium chamber constituting the first vibration isolating mechanism is in the state open to the open air, the diaphragm provided there freely vibrates. As a result, increase in the liquid pressure in the first liquid chamber is avoided against the entered vibration within the high frequency region, thus reducing the dynamic spring constant of this vibration isolating apparatus as a whole. This isolates vibration within the high frequency region which causes a dull sound.
In the present invention, as described above, the first equilibrium chamber and the second equilibrium chamber are independently kept in a negative pressure state or the atmospheric pressure state, or a negative pressure and the atmospheric pressure are alternately introduced at a specific cycle (frequency) into the first equilibrium chamber. As a result, a low dynamic spring constant is available over a wide range of frequency regions ranging from low-frequency vibration mainly comprising idling vibration to high-frequency vibration centering around the dull sound. Reduction of the dynamic spring constant thus permits isolation of idling vibration and vibration associated with the dull sound. Engine shake which is low-frequency vibration can be isolated (inhibited) by obtaining a high damping property.
In the vibration isolating apparatus of the above constitution of the present invention, the housing space is a side branch having a closed end. Therefore, the vibration isolating apparatus is surely provided according to the above constitution.
Furthermore, the vibration isolating apparatus of the present invention in another embodiment comprises a coupler attached to a vibrating body; a holder attached to the vehicle body side; an insulator provided between the coupler and the holder to absorb vibration from the vibrating body; a vibration isolator having a vibration isolating mechanism directly following the insulator and comprising a main liquid chamber having a wall thereof formed by a part of the insulator and sealing a liquid therein, an auxiliary liquid chamber connected to the main liquid chamber so as to cause the liquid to flow via an orifice, and an equilibrium chamber provided at a portion of the main liquid chamber via a diaphragm so as to change the volume thereof in the chamber; switching means performing a switching operation based on a frequency required for synchronizing with vibration of the vibrating body so as to introduce alternately a negative pressure from a negative pressure source and the atmospheric pressure from an atmospheric pressure inlet to the equilibrium chamber; and control means for controlling the switching means; wherein: a resistance for slowing down the introduction of the negative pressure or the atmospheric pressure into the equilibrium chamber is provided in the middle of a communicating path communicating between the switching means and the equilibrium chamber.
In the vibration isolating apparatus of the above configuration of the present invention, the housing space is a side branch having a closed end.
In the vibration isolating apparatus of the above configuration of the present invention, the effects substantially the same as those of the apparatus of the preceding configuration are available. A resistance is provided in the middle of a communicating path communicating between the switching means and the equilibrium chamber. The presence of this resistance slows down the increasing and decreasing rates of the pressure in the equilibrium chamber. Fluctuations of pressure in the equilibrium chamber therefore exhibit a smooth behavior, thus permitting control of fluctuations of the liquid pressure in the main liquid chamber in response to vibration of the vibrating body.
The liquid-sealing type vibration isolating apparatus of the present invention for achieving further another object thereof comprises an upper coupling member attached to a vibrating body; a lower coupling member attached to a member or the like on the vehicle body side; an insulator provided between the upper coupling member and the lower coupling member to absorb and isolate vibration from the vibrating body; a main chamber having a wall thereof formed by a part of the insulator and sealing a liquid; an auxiliary chamber connected to the main chamber via a first orifice and having a part of the wall thereof formed by a first diaphragm; a third liquid chamber connected to the main chamber via a second orifice and formed so as to receive the liquid in the main chamber; and an equilibrium chamber partitioned and formed by a second diaphragm having a higher spring constant than the first diaphragm relative to the third liquid chamber and receiving any one of the atmospheric pressure and a negative pressure; the liquid-sealing vibration type isolating apparatus further comprises switching means for performing a switching operation so as to alternately introduce any one of the negative pressure and the atmospheric pressure into the equilibrium chamber, in synchronization with engine vibration; and control means controlling the switching operation of the switching means.
By adopting the constitution as described above, the following functions are available in the present invention. As to idling vibration, a negative pressure and the atmospheric pressure are alternately introduced at a specific frequency into the equilibrium chamber by operating the switching means. More specifically, the pressure (volume) in the equilibrium chamber is altered by operating the switching means at a specific frequency to absorb fluctuations of the liquid pressure in the insulator and the main chamber caused by idling vibration entered through the insulator. As a result, there occurs a decrease in the dynamic spring constant of the spring system formed by the insulator and the vibration isolating mechanism. Particularly in the apparatus of the present invention, operation of the second diaphragm causes the second orifice having a prescribed volume to connect the third liquid chamber subjected to pressure fluctuations and the main chamber, and the liquid in the second orifice resonates with fluctuations of the liquid pressure of the liquid in the main chamber under the effect of operation of the equilibrium chamber, i.e., operation of the second diaphragm. Changes in the power generated (vibrating energy) for the entire vibration isolating mechanism are in a state of sine wave not containing high-frequency component noise, and this ensures absorption and isolation of idling vibration. It is also possible to avoid occurrence of high-frequency vibration which may accompany the isolation of idling vibration.
Regarding engine shake which is vibration of a frequency further lower than idling vibration, the liquid is caused to flow in the first orifice connecting the main chamber and the auxiliary chamber, thereby absorbing and isolating engine shake. More specifically, when vibration of engine shake is entered (vibration input) into the main chamber, the liquid in the main chamber receives pressure and acts to move the second diaphragm downward through the second orifice and the third liquid chamber. However, the second diaphragm forming the equilibrium chamber has become harder to deform with a higher spring constant than the first diaphragm forming part of the auxiliary chamber. Upon input of engine shake into the main chamber, therefore, the liquid in the main chamber flows through the first orifice toward the auxiliary chamber side prior to the deformation of the second diaphragm and to the volume change of the equilibrium chamber partitioned and formed by the second diaphragm. A high damping property (high damping force) is available from the flowing motion of the liquid in the first orifice, thereby inhibiting (damping) engine shake.
In the liquid-sealing type vibration isolating apparatus of the present invention as described above, a hardly deformable structure is adopted as a whole for the second diaphragm forming the equilibrium chamber. That is, in the liquid-sealing type vibration isolating apparatus, the second diaphragm has a constitution having stopper-like projections always in contact with both the partition plate forming the lower surface of the equilibrium chamber and the plate partitioning the main chamber and the third liquid chamber, these projections being arranged on the upper and lower sides near the center of the diaphragm. By adopting the constitution as described above, in the present invention, idling vibration is coped with by introducing any one of a negative pressure and the atmospheric pressure at a prescribed cycle into the equilibrium chamber through operation of the switching means. As a result, the second diaphragm deforms (displaces) under the effect of elastic deformation of the flat portion not containing projections, thereby vibrating the liquid in the third liquid chamber provided above the second diaphragm. This causes the vibrating force to propagate through the second orifice into the main chamber and acts to inhibit the increase in the liquid pressure in the main chamber. Reduction of the dynamic spring constant for the entire vibration isolating apparatus is thus accomplished upon input of idling vibration.
Engine shake is on the other hand coped with by bringing the equilibrium chamber into the state open to the open air through operation of the switching means. When engine shake is entered into the main chamber in this state, fluctuations of the liquid pressure in the main chamber are transmitted through the second orifice and the third liquid chamber to the second diaphragm in response thereto. The deformation region of the second diaphragm itself has however become narrower because of the presence of the projections, thus making it harder to deform (displace). The liquid in the main chamber therefore flows through the first orifice toward the auxiliary chamber having the wall thereof formed by the easily deformable first diaphragm. A high damping property (high damping force) of the vibration isolating apparatus is available from this flowing motion of the liquid to the first orifice. This high damping force inhibits (damps) the engine shake.
In the liquid-sealing type vibration isolating apparatus of the constitution described above, the construction around the second diaphragm partitioning the third liquid chamber from the equilibrium chamber comprises a rubber-film-like diaphragm, and a spring serving to always push back the rubber-film-like diaphragm toward the third liquid chamber. By adopting this constitution in the apparatus of the present invention, as in the preceding constitution, against idling vibration, an engine negative pressure and the atmospheric pressure are alternately introduced into the equilibrium chamber by operating the switching means, thereby causing the second diaphragm to deform in the state resisting to the spring reaction force and eventually preventing the liquid pressure in the main chamber from increasing. As a result, the dynamic spring constant for the vibration isolating apparatus as a whole is reduced upon input of idling vibration, thus permitting isolation of idling vibration.
To cope with engine shake, the pressure transmitted through the second orifice and the third liquid chamber to the second diaphragm is received with the spring reaction of the spring so as not to cause deformation (displacement) of the second diaphragm. As a result, the liquid in the main chamber flows through the first orifice toward the auxiliary chamber having the wall partially formed by the easily deformable first diaphragm. A high damping property is available from the flowing motion of the liquid in the main chamber into the first orifice, thus eventually accomplishing damping (inhibition) the engine shake.
Another liquid-sealing type vibration isolating apparatus of the present invention is characterized in that the vibration isolating mechanism is in a cylindrical shape. More specifically, the apparatus comprises an inner cylinder forming a coupler attached to a vibrating body and having a cylindrical shape; an outer cylinder forming a holder attached to the vehicle body side and having a cylindrical shape; an insulator provided around the inner cylinder between the inner cylinder and the outer cylinder; and a vibration isolating mechanism provided around the insulator and sealing a liquid which is an incompressible fluid; the vibration isolating mechanism comprising a main chamber having a wall thereof formed by a part of the insulator; an auxiliary chamber connected to the main chamber so as to allow the liquid to flow via an orifice and separated from the main chamber by a partition plate comprising a rigid body; an equilibrium chamber provided at a part of the main chamber via a diaphragm and formed so that the volume thereof in the chamber changes; and an air chamber provided outside the auxiliary chamber via another diaphragm and constantly receiving air; the cylindrical liquid-sealing type vibration isolating apparatus further comprising switching means performing a switching operation so as to cause continuous and alternate introduction of any one of a negative pressure and the atmospheric pressure in synchronization with engine vibration, and control means for controlling the switching operation of the switching means. By adopting this constitution of the present invention, it is possible to achieve further downsizing and reduction of weight, and to save the space for supporting the vibrating body.